Currently, both diagnostic and therapeutic catheters are manufactured by forming braided tubes of stainless steel fibers or strands, over a mandrel. More specifically, the braided tube may be formed about an inner Teflon.RTM. liner or tube initially carried on a supporting mandrel. An outer plastic layer may then be extruded about the braided material to create the catheter body. Current catheter constructions also utilize a transition tip which is not reinforced with braid in order that the tip be softer and more flexible than the remaining portions of the catheter. In some catheter designs, an even more flexible tip is bonded to the free end of the tubular transition tip.
Catheters which incorporate multiple axial sections typically employ butt or lap weld joints to secure the axial sections of the catheter together. See, for example, U.S. Pat. Nos. 5,254,107; 4,861,337; 4,793,351; 4,662,404; and 4,391,302.
Catheters incorporating either butt or lap type welded joints are not completely satisfactory however, and it is thus the object of this invention to improve upon prior catheter constructions by incorporating unique weld configurations which have a substantial axial seam component extending along the axis of the catheter. In other words, adjacent catheter sections are cut and welded in such a way that they overlap in the longitudinal direction, but without altering the outer diameter of the catheter. This arrangement not only increases surface area at the weld joints and thereby also increases bond integrity, but also creates a more desirable transition between the same materials of different durometer or different materials with or without the same durometer, than other more conventional welds such as lap or butt welds.
The unique weld configurations of this invention also permit alteration of properties or characteristics of the catheter material in the area of the weld, and this feature is particularly advantageous in areas of the catheter that will be curved, in that different stiffness or hardness materials can be used on the inside and outside of the curve.
Examples of the unique weld configurations in accordance with this invention include step joints, taper joints, and combinations of the two.
Thus, in accordance with its broader aspects, the present invention relates to a catheter having at least two lengths of tubular material axially joined together by a welded joint with no perceptible change in outer diameter at the welded joint; the welded joint including a substantial axially oriented seam between the two lengths of material.
In another aspect, the invention relates to a catheter having at least two lengths of tubular material axially joined by a welded joint, the welded joint having an axial length component of at least 0.5 cm. in length, and preferably in the range of 0.5-10 cm.
Other objects and advantages of the subject invention will become apparent from the detailed description which follows.